Not Applicable
1. Field of the Invention
The invention relates to emergency lighting, and particularly to fluorescent lighting wherein a fluorescent lamp is connected to a source of electrical energy other than normal AC line current in the event that the normal AC current fails.
Emergency lighting is required in commercial, industrial, and institutional buildings just as fire extinguishers, smoke alarms and other safety equipment. Three types of emergency lighting are common in such installations: unit equipment, engine generators and central battery systems. Unit equipment falls into two principle types: fluorescent and incandescent.
The fluorescent emergency units are customarily combined or within a conventional fluorescent lighting unit by merely adding the emergency ballast consisting of a battery, a battery charger, inverter and sensing circuitry adjacent the standard fluorescent AC ballast. The sensing circuit of the emergency ballast observes the interruption of normal AC power to the lamp unit and immediately switches on the emergency ballast to power individual lamp(s) or the light fixture for the required period. Under most state safety codes, this is a period of at least ninety (90) minutes, a standard called out in the National Electrical Code, NFPA Article 70, and NFPA Article 101 Light Safety Code.
2. General Background of the Invention
U.S. Pat. No. 5,004,953 entitled Emergency Lighting Ballast for Compact Fluorescent Lamps with Integral Starters, assigned to the assignee of the present invention is illustrative of the general fluorescent type of emergency lighting with a ballast. It is common in the installation of emergency fluorescent lighting that an emergency ballast is added to a conventional fluorescent fixture or provided integrally in a fixture having internal regular and emergency ballast installed. When main AC power fails, voltage sensing circuitry instantly connects DC current from a battery (in the emergency ballast) to an inverter which produces high frequency, high voltage power to illuminate the fluorescent lamp(s) in emergency mode for the required period.
The present invention is directed to fluorescent lighting fixtures which are likely to be exposed to extreme low temperatures wherein the battery which supplies the power for lighting when main AC power fails is apt to freeze. Until now, emergency lighting has been utilized in such as commercial an governmental buildings wherein it is unlikely that power will be out for such a long period of time that the batteries for providing the back-up power will freeze. The state of the art units typically are recommended for temperature ranges of about 0xc2x0 C. to about 50xc2x0 C. Unit contained emergency fluorescent lighting is now so reliable and common that it is being considered for such as smaller out buildings, garages, outside staircases and warehouses where the building (or fluorescent unit) is unheated, or if subjected to prolonged power outage during winter, the internal environment may cool to 0xc2x0 C. or lower. After a prolonged time at below freezing temperatures, the battery internal to the emergency ballast is likely to freeze. A problem arises when normal AC power is restored and the battery charging circuit of the unit attempts to recharge the battery. With the inclusion of the present invention, emergency fluorescent lighting may be extended to an operating range of about xe2x88x9220xc2x0 C. to about 50xc2x0 C.
It is known that rechargeable batteries such as the nickel-cadmium type typically used in fluorescent emergency lighting systems have difficulties in charging when frozen. Charging may be erratic, and at times at rates much higher than the rate recommended by manufacturers for safe operation. There is also a danger that during an erratic charging process that volatile gasses, particularly hydrogen, may build-up and pose the threat of explosion. The present invention provides a heating mechanism for the rechargeable battery which keeps it at a suitable charging temperature during normal operation whether the installation site building is heated or not, enabling the use of the unit in unheated or lesser heated facilities. Further, the heater circuit addition includes means for connecting the charging circuit to an alternate load while the battery comes up to suitable temperature for charging, while keeping the appropriate relays connected so that upon the resumption of AC power, the normal fluorescent lighting may be powered by the AC main power. Once the battery temperature is sensed to be at a sufficient level for safe charging, the charging current is switched to the battery from the alternate load so as to fully recharge the battery.
Those skilled in the art will recognize that alternative approaches to the preferred embodiments of the present invention disclosed herein may be made without departing from the scope of the present invention.
The present invention is directed to an emergency ballast for operation in extreme temperature conditions where the battery powering the emergency ballast and emergency fluorescent lamp becomes frozen and requires heating to a recognized minimum temperature before safe recharging may be initiated.
One of the objectives of the present invention is to cause the internal battery of the fluorescent emergency ballast to remain in its normal operating temperature range during when main AC power is supplied to the fluorescent lamp.
A further objective of the present invention is to delay the charging of the battery in the emergency ballast after a loss of main AC power during extreme cold wherein the internal temperature of the battery has dropped below the recommended operating temperature, or has frozen, and the battery is heated to a permissible operating range before recharging current is applied.
An alternate objective of the present invention is the inclusion of the described delay in charging the battery when its internal temperature is below recommended, and the inclusion of enabling circuitry to cause the fluorescent fixture to illuminate on the return of main AC power, irrespective of the ambient temperature.
These and other objectives will be evident from the detailed descriptions of the preferred embodiments provided below.